1. Field of the Invention
The present invention relates to an electric arc torch in which a power feeding member and a nozzle for covering the same are coaxially disposed at a tip portion of the torch body thereof and two detection means for detecting a mounted and dismounted state of the nozzle are provided each of which provides a detection pin slidable in parallel with the axis of the power feeding member.
2. Description of Prior Art
A plasma arc torch as shown in FIG. 16(A) or a consumable electrode type arc torch as shown in FIG. 16(B) is widely used as an electric arc torch for cutting or welding works. It invites a very dangerous state if the power is supplied to the power feeding member 2 in the state that the nozzle 3 has been dismounted to repair the arc torch. In order to avoid this, a detection means 4' is provided for detecting that the nozzle 3 is dismounted from the torch body of the arc torch 1 and, when it is detected thereby, the power supply is suspended for the safety of repair work.
FIGS. 16(A) and 16(B) show tip portions of conventional arc torches 1 having such a detection means 4', respectively and FIG. 16(C) shows the detection means 4' in an enlarged scale. The detection means 4, is comprised of a terminal element 6 to which an end of a conductor 5 is connected, a detection pin 7 slidable in the axial direction of the arc torch, a compression spring 8 inserted between the terminal element 6 and the detection pin 7 and an O-ring 9 acting as a stopper for the detection pin 7. One more detection means 4' (not shown) is arranged integrally with the torch body and diametrically opposed to the former one to form a pair of detection means 4' and 4'.
The mounted and dismounted state of the nozzle 3 can be detected by a contacted and discontacted state between the detection pin 7 and the nozzle 3. Namely, the detection pin 7 is moved in the upward direction Y.sub.2 against the spring force by the compression spring 8 when the nozzle 3 is mounted to the torch. On the upper end surface of the nozzle 3, an electrically conductive thin film (not shown) is formed and, therefore, two detection pins 7 of the pair of the detection means 4' and 4' are electrically conducted with each other by the conductive thin film as long as the nozzle 3 remains mounted.
On the contrary, when the nozzle 3 is dismounted from the torch body, two detection means 4' and 4' are electrically disconnected with each other and, thereby, a detection signal is generated. Due to this detection signal, the power supply to the power feeding element 2 is suspended. As stated above, the spring force applied to each detection pin 7 by the compression spring 8 is supported by the O-ring 9 functioning as a stopper for the pin in this state. In this context, it is impossible to omit the O-ring 9.
However, O-ring 9 is easily worn out due to the shearing force by the compression spring 8 and the heat exerted thereto during use of the torch.
Further, the conventional arc torch has disadvantages that the detection pin 7 cannot slide in the axial direction smoothly when itself or the guide means therefor is deformed accidentally by a strong external force and that the conductor 5 is cut off when a strong external force is applied to the torch.
Due to these reasons, it becomes necessary to frequently repair the detection means 4' and/or to change the O-ring 9 and, in the case that it becomes impossible to interchange the old one to a new one, the torch body supporting the detection means 4' and 4' integrally has to be replaced with a new one.